1. Field of the Invention
The present invention generally relates to a magnetic disk device, and more particularly to a magnetic disk device which includes an actuator moving the magnetic head between the innermost positions of the data zone of the magnetic disk and the outermost position of the data zone thereof.
2. Description of the Related Art
In a magnetic disk device that performs recording or reproduction of information to the magnetic disk, it is necessary to avoid wearing of the head slider (the magnetic head) by the contact between the head slider and the magnetic disk surface.
Therefore, the contact start-stop (CSS) method is adopted in which the head slider contacts the disk surface only at the time of non-operation of the magnetic disk device, and the head slider is raised over the surface of the magnetic disk during its rotation at the time of operation of the magnetic disk device (or the time of recording or reproduction of information).
In the magnetic disk device of the CSS method, the head slider which carries the magnetic head which performs recording or reproduction of information to the magnetic disk surface is raised by receiving the air flow which is created by the rotation of the magnetic disk at the time of operation of the magnetic disk device.
And when recording or reproducing information to the magnetic disk, the head slider is moved with the actuator while being raised over the surface of the rotating magnetic disk and the head slider is positioned on the predetermined track of the magnetic disk.
Specifically, a data zone is formed in the magnetic disk, and the magnetic head is moved between the innermost position of the data zone of the disk and the outermost position of the data zone of the disk by the actuator. For example, this is known from Japanese Laid-Open Patent Application No. 2001-035103.
On the other hand, when the magnetic disk device is in the non-operating state, the head slider is located on the CSS zone which is formed in the surface of the magnetic disk. Moreover, the rotation of the magnetic disk is stopped when the magnetic disk device is in the non-operating state, the air flow which serves to raise the head slider is not created, and the head slider is in contact with the CSS zone of the disk.
The CSS zone may be formed at either the disk inner peripheral position that is located inside the innermost position of the data zone of the magnetic disk, or the disk outer peripheral position that is located outside the outermost position of the data zone of the magnetic disk. Usually, the CSS zone is formed at the disk inner position.
A description will now be given of a conventional magnetic head device 100 by using FIG. 1 through FIG. 7.
FIG. 1 is a plan view of the conventional magnetic head device 100 when the head slider is located in the innermost position of the data zone of a magnetic disk. FIG. 2 is a plan view of the conventional magnetic head device 100 when the head slider is located in the outermost position of the data zone of the magnetic disk. Only the portion of the conventional magnetic head device 100 near the actuator 122 is illustrated.
As shown in FIG. 1 and FIG. 2, the actuator 122 which supports the head slider 104 on which the magnetic head is carried is rotatably supported on the supporting shaft 140 such that the actuator 122 is capable of being swung around the center of the supporting shaft 140.
The head slider 104 is formed with the support arm 124 and the support spring 125 in the front-end portion of the actuator 122 which is located in the front direction from the supporting shaft 140.
On the other hand, in the rear-end portion of the actuator 122 which is located in the rear direction from the supporting shaft 140, the coil arm 152 is formed with the actuator 122. The voice coil 151 is mounted on the coil arm 152.
As shown in FIG. 4, the voice coil 151 is provided so that the voice coil 151 is located in the magnetic field which is created with the upper magnet 156 provided on the undersurface of the upper yoke 154 and the lower magnet 155 provided on the upper surface of the lower yoke 153.
The voice-coil motor (VCM) 123 is constituted to swing the actuator 122 by means of the voice coil 151, the lower yoke 153, the upper yoke 154, the lower magnet 155, and the upper magnet 156.
Moreover, the magnetic disk 101 is rotated at the predetermined rotational speed by the spindle motor 112.
The data zone 132 is formed in the magnetic disk 101. Therefore, the head slider 104 is moved between the outermost position “Po” of the data zone 132 of the disk and the innermost position “Pi” of the data zone 132 of the disk. Moreover, the CSS zone 131 is further formed in the disk inner peripheral position that is located inside the innermost position Pi of the magnetic disk 101.
FIG. 3 is an enlarged view of the actuator 122 which is provided in the conventional magnetic head device 100. As shown in FIG. 3, the voice coil 151 which constitutes part of the voice-coil motor 123 is attached to the coil arm 152, and the voice coil 151 is arranged in a generally trapezoidal configuration. The actuator 122 of FIG. 3 is provided so that the intersection of the extension lines (indicated by the arrows B1 and B2 in FIG. 3) of the side section coils 151A and 151B of the voice coil 151 is in agreement with the rotation center (or the center of the supporting shaft 140) of the actuator 122.
FIG. 6 shows the composition of the upper and lower magnets 155 and 156 which constitute part of the voice-coil motor 123 in the conventional magnetic head device 100. In FIG. 6, only the lower magnet 155 is shown for the sake of convenience of illustration, but the upper magnet 156 which has the same composition as the lower magnet 155 is also provided.
The lower magnet 155 is composed of the north-pole magnet section 155N and the south-pole magnet section 155S, and this north-pole magnet section 155N and this south-pole magnet section 155S confront each other (hereinafter, the position where the north-pole magnet section 155N and the south-pole magnet section 155S confront each other is called the magnetization center 158).
Conventionally, the magnet 155 is provided such that the north-pole magnet section 155N and the south-pole magnet section 155S are arranged in a symmetrical formation with respect to the magnetization center 158. That is, the deviation (which is indicated as the rotational angle TN in FIG. 6) of the right side section of the lower magnet 155 from the magnetization center 158 and the deviation (which is indicated as the rotational angle TS in FIG. 6) of the left side section of the lower magnet 155 from the magnetization center 158 are equal to each other (TN=TS).
In addition, the stoppers 127A and 127B are arranged at both the side positions of the voice-coil motor 123, and the voice-coil motor 123 is provided to prevent the excessive swinging of the actuator 122 around the center of the supporting shaft 140 to exceed the predetermined stop position.
As shown in FIG. 4, the lower magnet 155 and the upper magnet 156 are arranged so that the north-pole magnet section 155N of the lower magnet 155 and the south-pole magnet section 156S of the upper magnet 156 are opposed to each other, and the south-pole magnet section 155S of the lower magnet 155 and the north-pole magnet section 156N of the upper magnet 156 are opposed to each other.
For this reason, fundamentally, the perpendicular magnetism in the vertical direction in FIG. 4 is created between the lower magnet 155 and the upper magnet 156. When the voice coil 151 is located within this perpendicular magnetism, the force (the driving force) in the horizontal direction in FIG. 4 occurs on the voice coil 151 according to Fleming's left-hand rule. The actuator 122 is swung around the center of the supporting shaft 140 in accordance with this driving force.
FIG. 5 is an enlarged view of the magnetization centers 158 and 159 of the upper and lower magnets 155 and 156. In FIG. 5, the arrow indicates the line of the magnetic force of the magnetism generated with the magnets 155 and 156.
As is apparent form FIG. 5, in the vicinity of the magnetization centers 158 and 159 of the magnets 155 and 156, the lines of the magnetic force are not formed exactly in the vertical direction (or the vertical direction in FIG. 5), and the magnetic field is slightly inclined to the vertical direction.
Therefore, when the voice coil 151 passes through the region where this inclined magnetic field is formed, the driving force generated according to Fleming's left-hand rule may contain not only the component in the horizontal direction but also the component inclined to the vertical direction (hereinafter, such a component of the driving force will be called the unnecessary driving force). Therefore, when the unnecessary driving force is applied to the voice coil 151, some vibration may occur in the actuator 22.
In the conventional magnetic head device 100, as shown in FIG. 1, when the head slider 104 is located at the innermost position Pi of the data zone, the center C of the voice coil 151 is deviated slightly upward from the magnetization center 158 (the angle “T1i” in FIG. 1 indicates the amount of deviation).
Moreover, as shown in FIG. 2, when the head slider 104 is located at the outermost position Po of the data zone, the center C of the voice coil 151 is deviated slightly downward from the magnetization center 158 (the angle “T1o” in FIG. 2 indicates the amount of deviation).
The conventional magnetic head device 100 is provided such that these amounts of deviation are set to meet the condition: T1o>T1i. That is, the conventional magnetic head device 100 is provided such that, when the head slider 104 is located at the innermost position Pi, the right side section coil 151A (which is shown in FIG. 7) is located nearer to the magnetization center 158 than the left side section coil 151B.
FIG. 7 is a diagram for explaining the problem of the conventional magnetic head device 100.
In FIG. 7, both the position (indicated by the solid line) of the voice coil 151 on the magnet 55 when the head slider 104 is located at the innermost position Pi, and the position (indicated by the one-dot chain line) of the voice coil 151 when the head slider 104 is located at the outermost position Po are shown.
As shown in FIG. 7, the deviation (T2o) between the magnetization center 158 and the side section coil 151A when the head slider 104 is located at the outermost position Po is smaller than the deviation (T2i) between the magnetization center 158 and the side section coil 151B of the voice coil 151 when the head slider 104 is located at the innermost position Pi (T2i>T2o).
Thus, in the conventional magnetic head device 100, when the head slider 104 is located at the outermost position Po, the side section coil 151A is located within the region in which the lines of magnetic force generated near the magnetization center 158 are inclined to the vertical direction.
For this reason, in addition to the horizontal force (the driving force for the actuator 122), the unnecessary driving force will be applied to the side section coil 151A, and some vibrations occur on the actuator 122.
Thus, when the vibrations occur on the actuator 122, the head slider 104 may be impacted with the magnetic disk 101. Hence, the problem arises in that there is the possibility that the information recorded in the data zone 132 may be damaged in the worst case.